RADIOSENSITIVITY OF HAPLONT YEAST-CELLS IRRADIATED WITH SPARSELY AND DENSELY IONIZING-RADIATIONS

Five haploid and three diploid yeast strains of various species (Yarro wia lipolytica, Pichia pinus and Pichia guilliermondii) were irradiate d with alpha-particles from Pu-239 and gamma-rays from Cs-137 Or Co-60 in the stationary phase of growth. A common feature of these species is that they exhibit a haploid stare as a normal vegetative state in n atural conditions, It was shown that the transition from the haploid t o the diploid state is not accompanied by increased radioresistance, a nd diploid strains were unable to perform liquid-holding recovery. The absence of diploid-specific recovery in diploid strains was also supp orted by the fact that the RBE of alpha-particles was almost identical for haploid and the corresponding diploid strains being much smaller than that observed in typical wild-type diploid strains capable of dip loid-specific recovery. The results suggest that haplont yeast may hav e evolved to diplont yeast via the development of a specific repair sy stem conferring specific resistance in the diploid state.